1. Field of the Invention
The present invention relates to a scanning light exposure apparatus, and more particularly to a light exposure apparatus suitable for the exposure of light to a large size board such as a liquid crystal display board.
2. Related Background Art
A quality of a liquid crystal display panel has recently been significantly improved, and because of its thinness and light weight, it has been widely used in place of a CRT. Particularly, in an active matrix type direct view liquid crystal panel, a screen size has been increases and a size of a glass board used for the manufacture thereof has also been increased.
As a light exposure apparatus for exposing a light to such a large size glass substrate, a so-called proximity system in which a mask and a substrate are placed in proximity and a light is exposed collectively, a step and repeat system which uses a diffraction optical system of unity magnification having a large transfer area as a projection optical system, or a mirror projection system in which a projection optical system is a reflection optical system of unity magnification and a mask is illuminated by an arcuate illumination light and an arcuate image of the mask is formed on a substrate, and the mask and the substrate are scanned relative to the projection optical system.
When a large size substrate is exposed in the proximity system, it is necessary to proximate the mask which is large in size in accordance with the substrate size to the substrate to several tens microns. As a result, the mask and the substrate contact to each other because of unevenness of the mask and the substrate, the unevenness of the surface of a resist applied to the substrate or the dusts deposited on the surface thereof, and hence it has been difficult to transfer the mask pattern to the entire surface of the substrate without defect. Further, since a spacing between the mask and the substrate materially affects to a resolution of the image transferred, a line width and a line shape, it does not fit to the manufacture of the active matrix liquid crystal panel or a fine STN liquid crystal panel unless the spacing is uniformly designed.
In the step and repeat system, a reticle of approximately 6 inches which is smaller than the substrate is used as a mask and it is transferred to the large size substrate by the step and repeat. Since the step and repeat system permits the use of the reticle used in the manufacture of a semiconductor device as a mask, the techniques developed in the manufacture of the semiconductor device such as a draw precision, a pattern size control and dust processing can be used. However, in the transfer to the large size substrate, in order to expose a light beyond an area of an effective projection area (image circle), a so-called split exposure system in which a transfer area of the substrate is split into sub-areas for light exposure must be adopted. However, in the active matrix liquid crystal panel display, when there is a slight deviation in a boundary area of the pattern formed by the split light exposure, the performance of the element in that area will change, which causes a variation in density on the completed liquid crystal panel. This is easily visually recognized by human beings and it is a defect in the display quality of the liquid crystal display panel. The larger the number of splits is, the larger is the number of times of light exposure and it is necessary to exchange the reticle many times during the exposure of one substrate. This will lower the processing capability of the apparatus.
In the mirror projection system, since the entire surface of the mask is transferred to the substrate by scanning the arcuate slit extending transversely to the scan direction of the mask and the substrate relative to the mask and the substrate, it is necessary that the length of the slit is as long as the dimension of the substrate in order to efficiently expose the light to the large size substrate. As a result, it is necessary that the optical system is of large scale and the apparatus becomes large, which causes the increase of cost.